Generally, the wafers are moved into the furnace by the carrier. There is a carrier I.sub.(input) /O.sub.(output) port on the furnace. FIG. 1 shows the front view of the furnace. From the FIG. 1, the carrier I/O port is located on the middle position of the furnace. It is the rectangular opening for placing two carriers 14. A stage is under the carrier I/O port and as a base to support the carrier. There are two sets of orientation flat aligner in the stage 15. FIG. 2 shows the cross-section view of the furnace. FIG. 3 shows the cross-section view of magnifying the stage 15 and the carrier I/O port. The carrier 14 includes one cassette and four piers. There is a photosensor bracket among the four piers. The stage includes two orientation flat aligners 20.
FIG. 4 shows the front view ofthe orientation flat aligner. An orientation flat aligner includes four devices: one fixed shell 22, two rollers 24, wafer counters 26, and a driver 28. The driver 28 contains a ring roller 30 connected to the power supplier of the furnace and a belt tied with the driving roller and the two rollers as shown in FIG. 5. When the power supplier supplies the energy to the driving roller, the driving roller will rotate and drive the two rollers to work by the belt. FIG. 6 shows the top view of the orientation flat aligner. The outline oftwo rollers is serrated from the FIG. 6. This is because the rollers 24 combine with two different radius rings, as shown in FIG. 7. Generally, the wafers were placed on the depressed part of the roller and secured by the bigger rings of the roller. The stage 15 is a hollow fixed structure. An orientation flat aligner 20 will be elevated from the stage to the photosensor bracket 19 when the orientation flat aligner begin work. The photosensor bracket includes a photosensor 32 and a reflecting plate 34. When the orientation fiat aligner is elevated, the rollers will raise the wafers up a little bit to rotate the wafers to made the flat edge of the wafers line up. After the fiat edge ofthe wafers lines up, the orientation flat aligner will move down to the stage position and then the photosensor employ infrared ray to check the result. If the flat edge of the wafers line up, the infrared ray can reach the reflecting plate 34 through the path 33 and reflect back the photosensor through the path 35, as shown in FIG. 8.
The operating procedure of conventional orientation flat aligner of the furnace: (1) Put carrier into the carrier I/O port. (2) Elevate the orientation fiat aligner to the upstage position, the position of photosensor bracket. (3) Rotate the parallel rollers of orientation flat aligner about forty seconds. (4) Count the number of the wafers by the wafer counters. (5) Move the orientation flat aligner down to the stage position. (6) Check the flat edge of the wafers by the photosensor on the photosensor bracket. (7) If the flat edge of the wafers do not line up, repeat the procedure from the second step to the sixth step until the the flat edge of the wafers line up. After the flat edge of the wafers line up, the wafers are loaded on the boat to continent the next process.
There are two disadvantages about the conventional orientation flat aligner. One is the two parallel rollers with the same size. In normal condition, when the flat edge of the wafers line up, there are two degree angle deviation occurred on the right hand by arrows 37 in the FIG. 9. Ifthe flat edge ofthe wafer has touched on the rollers when the wafer loaded on the carrier were placed into the carrier I/O port, it is no useful to rotate roller to make the flat edge of the wafer reach the correct position. Thus, the undesired condition will happen as shown in FIG. 10. The undesired condition is that the angle deviation about two degrees occur on the left hand, indicated by arrow 38. This condition will make the wafers drop or break when the flow rate of gas is too strong or the boat moves in the furnace. The another is the photosensor located on the photosensor bracket. The photosensor detect the the flat edge of the wafers whether the flat edge of the wafers line up or not, after the rollers stop rotating and then the orientation flat aligner move back the stage. If the flat edge of the wafers do not line up, repeat the procedure from the second step to the sixth step until the flat edge of the wafers line up. This design which the photosensor are not separated from the orientation flat aligner wastes time for checking the flat edge ofthe wafers and increases the mis -detection chance to damage the wafers.